Optical properties of vertically aligned graphene sheets
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Optical properties of vertically aligned graphene sheets Takatoshi Yamada1, 2*, Makoto Hisa2 and Masataka Hasegawa1, 2 1 National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1, Higashi, Tsukuba, Ibaraki, 305-8565, JAPAN. 2 Technology Research Association for Single Wall Carbon Nanotube (TASC), 1-1-1, Higashi, Tsukuba, Ibaraki, 305-8565, JAPAN. *[email protected] ABSTRACT We have developed deposition of vertically aligned graphene sheets on Cu foils by surface wave microwave plasma CVD and the transfer from Cu foil to quartz substrate to evaluate optical reflectances and transmittances of the inherent vertical aligned graphene sheets. Both reflectance and transmittance spectra are almost independent of incident angles in the range between 300 and 800nm. The reflectance is lower than 0.067%, which is lower than those of the commercial black alumite plate. The transmittances are less than the detection limit of the system. It is considered that the obtained low reflectance is attributed to the unique structure of the vertically aligned graphene sheets. INTRODUCTION Graphene has almost flat optical absorption in a wide range of wavelengths, therefore transparent conductive films based on graphene are fabricated and touch screen and light emitting devices are demonstrated [1-3]. On the other hand, low reflectance applications using graphene nanostructure array are proposed [4]. The reflectance of the fabricated graphene nanostructure array was almost the same as that of single wall carbon nanotube (SWCNT) [5]. In addition, it is well known that graphene has high thermal conductivity. Therefore, the graphene nanostructures are expected to be one of the most appropriate low-reflectance materials, which can improve sensitivity and resolution of microscopies, spectrometers and telescopes. Graphene nanostructure arrays were fabricated by plasma etching of bulk graphite at 600 ºC [4] and SWCNT forests were grown on Si substrate at 750 ºC [5]. Because of such a high temperature to form the structures, it is difficult to form these carbon structures on various substrates, which is one of the issues to be solved toward practical applications. Furthermore, the reported low reflective properties were evaluated from the graphene nanostructures on bulk graphite substrates and SWCNT forests on Si substrates. In order to understand the inherent optical properties of carbon nanostructures, the optical properties should be evaluated after removing the substrate. Vertically aligned graphene sheets and/or carbon nanowalls, synthesized by plasma chemical vapor deposition (CVD) [6, 7], have structures similar to the graphene nanostructure array [4]. The vertically aligned carbon nanostructures are expected to have low reflectances. Although they have attracted much attention as field emitters, battery applications and sensors, optical properties of vertically aligned carbon nanostructures have not yet been understood. Furthermore, it would be possible to reduce the temperature to form graphene nanostructures
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